This invention relates to excess flow valves for controlling flow through a conduit and more particularly to an excess flow valve that minimizes pressure drops within the valve through a simplified valve construction.
Excess flow valves are utilized to limit the amount of fluid flow through a conduit. Generally, some way of holding the valve in a generally open position maintains the valve in an open position, allowing flow through the conduit if the flow rate through the conduit is below a predetermined limit. If the flow rate increases causing the pressure drop across the valve to exceed a certain value, then the valve is moved to a closed position restricting flow through the conduit.
One type of excess flow valve uses a magnet to hold the valve at a generally open position. The typical prior art magnetic excess flow valve has been incorporated into a capsule, wherein the entire structure for providing a valve seat, a valve guide, and a magnet holder are all incorporated as a single capsule item. Ideally, any pressure drops across the valve will help close the valve. Prior art valve structures are inefficient, however, because the structures often interfere with fluid flow through the valve, causing excessive pressure drops that do not aid in closing the valve. Further, even though magnets should have sufficient force to re-open a closed valve, current magnet structures may not always have force characteristics that also allow the attractive force to be minimized in the open position to improve the sensitivity of the valve plate for valve closing.
In addition, prior art valves have had non-symmetric structures, making valve operation dependent on the orientation between valve components. This causes the pressure drop required to close the valve to be, undesirably, a function of both the valve's component orientation and the flow rate rather than a function of the flow rate alone. When fluid pressure drops are a function of the orientation of components within the valve as well as fluid flow, the valve operation becomes unpredictable.
There is a desire for an excess flow valve structure that does not interfere with fluid flow and responds accurately and consistently to fluid pressure drops in a conduit.
There is also a desire for an excess flow valve structure that optimizes pressure drops to maximum valve efficiency while still maintaining a desired valve closure flow rate.